It would seem we have many more clients using NFC Automation on their iPhones these days and it would seem to be fragile. Linking the automation to the NFC tag seems fine, but when you try to tap a tag it sometimes works and other times it does not. Once it stops working it is difficult to get it working again. We have proved many times that using the tag and iPhone without the automation works fine and looking online there many posts about issues. So be aware of this if you hit issues. An example of a post is here: 

https://www.reddit.com/r/shortcuts/comments/pzgdf3/im_having_a_problem_with_automations_set_to/

Some fixes mentioned are to reboot the phone and also to delete and reinstate the NFC Automation - but will not always fix the problem that seems a little gremlin!

If you use a standard app like NFC Tools and just read the tag you can prove to yourself the tag is good and the issue is the NFC Automation.